Just place one edge of the bottle cap on top of the table, hold the neck of the bottle tight, and use your other hand to slam down on the bottle. It may take a few taps, but if you're a pro, the cap will pop off on your first try.
Place a paper napkin or a paper towel on top of the bottle cap. Then put a quarter on top of the napkin. When you use the bottle opener, the quarter will keep the middle of the cap from bending or creasing, and the napkin will keep the bottle cap free from scratches or gouges.